The current invention concerns an apparatus and method for adapting an exhaust flow guide having an enlarged diameter to an existing steam turbine inner cylinder. More specifically, the current invention concerns a multi-segmented mounting ring which allows an oversized exhaust flow guide to be securely mounted and accurately aligned to an existing inner cylinder and which provides a moisture removable slot upstream of the last row of blades.
The power output of an existing low pressure steam turbine can be increased by a retrofit which includes increasing the length of the last row of rotating blades. However, since such blades are enclosed by an exhaust flow guide, the original flow guide must be replaced by an oversized one--that is, an exhaust flow guide having a enlarged diameter. Unfortunately, as a result of its larger diameter, the oversized exhaust flow guide cannot be mounted onto the inner cylinder by bolting it to the face of the inner cylinder, as was done with the original exhaust flow guide.
One method for adapting an oversized exhaust flow guide to an existing inner cylinder is disclosed in U.S. Pat. No. 4,900,223, assigned to the same assignee as the current invention. According to this approach, a spacer is installed between the exhaust flow guide and the inner cylinder. The spacer is supported by, and aligned to, the inner cylinder by an undercut, formed on the inner diameter of the spacer, which rests against the outside diameter of the inner cylinder. The spacer is also supported by bosses welded to the end wall of the inner cylinder.
Unfortunately, the approach disclosed in U.S. Pat. No. 4,900,223 suffers from several drawbacks. First, resting the spacer ring against the outside diameter of the inner cylinder does not provide an accurate surface for aligning the spacer, and hence the exhaust flow guide. This is so because the outer diameter of the inner cylinder is not accurately located as a result of the inner cylinder being a fabricated component. Second, since the inner cylinder end wall is also not accurately located, the bushings welded to it may not be axially aligned around the circumference, thereby providing a non-uniform support surface for the exhaust flow guide. Third, no means are provided for removing moisture from the steam upstream of the last row blades, so as to avoid erosion of the blade tips.
Consequently, it would be desirable to provide an apparatus and method for adapting an enlarged diameter exhaust flow guide to an existing steam turbine inner cylinder which allowed accurate alignment and uniform support of the exhaust flow guide and which provided for moisture removable upstream of the last row rotating blades.